Christos A. Papageorgiou

An obstacle-aware human mobility model for ad hoc networks

In this work we present an obstacle-aware human mobility model for ad hoc networks. Typical examples where the nodes of mobile ad hoc networks are human-operated are natural or man-made disasters, military activities or healthcare services. In these scenarios, obstacles are an integral part of the areas where such networks are deployed in order to facilitate communication among the firemen, policemen, medics, soldiers, etc. In the proposed mobility model, the nodes of the network move around the obstacles in a natural and realistic way. A recursive procedure is followed by each node according to which every time an obstacle is encountered between the nodes current position and the final destination point, the node moves to the obstacles vertex that is closest to the destination. This process is repeated until the destination is reached. The obstacles are also taken into account in modeling the signal propagation. When a packet is transmitted through an obstacle, the power at which it is received is attenuated by a certain value representing the physical layer phenomena suffered by the signal. The model is implemented as an add-on module in Network Simulator ns-2. A thorough simulation study conducted highlights the differences of the proposed model with other mobility models, by investigating the properties of the resulting network topologies and their impact on network performance.

Simulating mission critical mobile ad hoc networks

In this paper we present a mobility model for ad hoc networks operating in mission critical situations, like for example natural or man-made disasters, military activities or emergency healthcare services. The proposed model captures the properties of mobility in situations like the above by incorporating hierarchical node organisation, typical for such scenarios modes of node activity, event-based destination selection and presence of physical obstacles that affect both the node movement and the signal propagation. The nodes are divided into groups with each group leader responsible for choosing the destination points. These choices resemble the events that occur in the network deployment area and the corresponding missions that are assigned to the node groups. The proposed model includes two modes of node activity that represent the two types of nodes primarily comprising such networks: the emergency workers and the medical staff. Each event belongs to a certain class, according to which reinforcements are called to provide further assistance. The conducted simulation study highlights the differences between the proposed model and other mobility models, by investigating their properties in terms of the resulting network topology and their impact on the performance of an ad hoc network operating under a well known routing protocol.

Modeling human mobility in obstacle-constrained ad hoc networks

In this paper we present a mobility model for ad hoc networks consisting of human-operated nodes that are deployed in obstacle-constrained environments. According to this model, the network nodes move around the obstacles in a way that resembles how humans bypass physical obstructions. A recursive procedure is executed by each node at its current position to determine the next intermediate destination point until the final destination point is reached. The proposed mobility model is validated using real-life trace data and studied using both mathematical analysis and simulations. Furthermore, the model is extended to incorporate several operational aspects of ad hoc networks in mission critical scenarios, where it is best applicable. These extensions include hierarchical node organization, distinct modes of node activity, event-based destination selection and impact of the physical obstacles on signal propagation. The model is implemented as an add-on module in Network Simulator (ns-2).

Security model for emergency real-time communications in autonomous networks

Towards the proliferation of architectures, tools and applications that have the potential to be used during an emergency rescue mission, we present a framework for emergency real-time communication using autonomous networks, called emergency Mobile Ad-hoc Networks (eMANETs). By eMANETs we refer to networks that are deployed in emergency cases where default telecommunications infrastructure has failed. Our goal is to design a security framework that will secure real-time communications during emergency rescue scenarios. The proposed framework consists of a secure routing protocol, intrusion detection provision and security extension for real-time communications using peer-to-peer overlays. We envisage that the results of this work will aid and serve the needs of any society against any event that threatens serious damage to human welfare or to the environment.

Energy-aware routing in wireless ad-hoc networks

We study energy efficient routing strategies for wireless ad-hoc networks. In this kind of network, energy is a scarce resource and its conservation and efficient use is a major issue. Our strategy follows the multi-cost routing approach, according to which a cost vector of various parameters is assigned to each link. The parameters of interest are the number of hops on a path, and the residual energy and transmission power of the nodes on the path. These parameters are combined in various optimization functions, corresponding to different routing algorithms, for selecting the optimal path. We evaluate the routing algorithms proposed in a number of scenarios, with respect to energy consumption, throughput and other performance parameters of interest. From the experiments conducted, we conclude that routing algorithms that take into account energy related parameters, increase the lifetime of the network, while achieving better performance than other approaches, such as minimum hop routing.

Energy-efficient multicasting in wireless networks with fixed node transmission power

In this work, we propose an energy-efficient multicasting algorithm for wireless networks for the case where the transmission powers of the nodes are fixed. Our algorithm is based on the multicost approach and selects an optimal energy-efficient set of nodes for multicasting, taking into account: i) the node residual energies, ii) the transmission powers used by the nodes, and iii) the set of nodes covered. Our algorithm is optimal, in the sense that it can optimize any desired function of the total power consumed by the multicasting task and the minimum of the current residual energies of the nodes, provided that the optimization function is monotonic in each of these parameters. Our optimal algorithm has non-polynomial complexity, thus, we propose a relaxation producing a near-optimal solution in polynomial time. The performance results obtained show that the proposed algorithms outperform established solutions for energy-aware multicasting, with respect to both energy consumption and network lifetime. Moreover, it is shown that the near-optimal multicost algorithm obtains most of the performance benefits of the optimal multicost algorithm at a smaller computational overhead.

Multicost routing over an infinite time horizon in energy and capacity constrained wireless ad-hoc networks

In this work we study the dynamic one-to-one communication problem in energy- and capacity-constrained wireless ad-hoc networks. The performance of such networks is evaluated under random traffic generation and continuous energy recharging at the nodes over an infinite-time horizon. We are interested in the maximum throughput that can be sustained by the network with the node queues being finite and in the average packet delay for a given throughput. We propose a multicost energy-aware routing algorithm and compare its performance to that of minimum-hop routing. The results of our experiments show that generally the energy-aware algorithm achieves a higher maximum throughput than the minimum-hop algorithm. More specifically, when the network is mainly energy-constrained and for the 2-dimensional topology considered, the throughput of the proposed energy-aware routing algorithm is found to be almost twice that of the minimum-hop algorithm.

Multicost Routing in Wireless AD-HOC Networks with Variable Transmission Power

In this work we study the combination of multicost routing and variable transmission power in wireless ad-hoc networks. In multicost routing, each link is assigned a cost vector consisting of several parameters. These parameters are treated separately and are combined at the end of the algorithm using various optimization functions, corresponding to different routing schemes, for selecting the optimal path. The cost parameters we use are the hop count, the interference caused, the node residual energies, and the node transmission powers. We assume that nodes can use power control to adjust their transmission power to the desired level. The experiments conducted show that the combination of multicost routing and adjustable transmission power can lead to reduced interference and energy consumption, improving network performance and lifetime.

Multi-cost routing for energy and capacity constrained wireless mesh networks

We propose a class of novel energy-efficient multi-cost routing algorithms for wireless mesh networks, and evaluate their performance. In multi-cost routing, a vector of cost parameters is assigned to each network link, from which the cost vectors of candidate paths are calculated using appropriate operators. In the end these parameters are combined in various optimization functions, corresponding to different routing algorithms, for selecting the optimal path. We evaluate the performance of the proposed energy-aware multi-cost routing algorithms under two models. In the network evacuation model, the network starts with a number of packets that have to be transmitted and an amount of energy per node, and the objective is to serve the packets in the smallest number of steps, or serve as many packets as possible before the energy is depleted. In the dynamic one-to-one communication model, new data packets are generated continuously and nodes are capable of recharging their energy periodically, over an infinite time horizon, and we are interested in the maximum achievable steady-state throughput, the packet delay, and the energy consumption. Our results show that energy-aware multi-cost routing increases the lifetime of the network and achieves better overall network performance than other approaches. Copyright

Joint multi-cost routing and power control in wireless ad hoc networks

In this work we study the combination of multi-cost routing and adjustable transmission power in wireless ad hoc networks, so as to obtain dynamic energy- and interference-efficient routes to optimize network performance. In multi-cost routing, a vector of cost parameters is assigned to each network link, from which the cost vectors of candidate paths are calculated. Only at the end these parameters are combined in various optimization functions, corresponding to different routing algorithms, for selecting the optimal path. The multi-cost routing problem is a generalization of the multi-constrained problem, where no constraints exist, and is also significantly more powerful than single-cost routing. Since energy is an important limitation of wireless communications, the cost parameters considered are the number of hops, the interference caused, the residual energy and the transmission power of the nodes on the path; other parameters could also be included, as desired. We assume that nodes can use power control to adjust their transmission power to the desired level. The experiments conducted show that the combination of multi-cost routing and adjustable transmission power can lead to reduced interference and energy consumption, improving network performance and lifetime.